where \(T_0(x)=1\)  and \(T_1(x)=x\)  [1]}.
Similarly, a filter \(g_\theta \)  can be computed by Chebyshev polynomial approximation, \(T_k\) , up to order \(K-1\) .
In this case, \(g_\theta \)  can filter \(\mathbf {x}\)  using the following equation:
\( \mathbf {y} = g_\theta \ast _\mathcal {G}\mathbf {x} = \sum _{k=0}^{K-1} \theta _k T_k(\tilde{L}) \mathbf {x},\) 
